QUESTION: Does neurodegenerative disease underlie the increased rate of dementia observed in older people with schizophrenia? Several studies have reported a higher prevalence of dementia in people with schizophrenia compared with the general population. This may reflect a higher risk of developing neurodegenerative diseases such as vascular dementia or Alzheimer's disease (AD). Alternatively, this may reflect non-pathological, age-related cognitive decline in a population with low cognitive reserve. STUDY SELECTION AND ANALYSIS: We reviewed papers that compared postmortem findings, hippocampal MRI volume or cerebrospinal fluid (CSF) markers of AD, between patients with schizophrenia with evidence of cognitive impairment (age ≥45 years) with controls. We subsequently performed a meta-analysis of postmortem studies that compared amyloid-ß plaques (APs) or neurofibrillary tangles (NFTs) in cognitively impaired patients with schizophrenia to normal controls or an AD group. FINDINGS: No studies found a significant increase of APs or NFTs in cognitively impaired patients with schizophrenia compared with controls. All postmortem studies that compared APs or NFTs in patients with schizophrenia to an AD group found significantly more APs or NFTs in AD. No studies found a significant differences in CSF total tau or phosphorylated tau between patients with schizophrenia and controls. The two studies which compared CSF Aß42 between patients with schizophrenia and controls found significantly decreased CSF Aß42 in schizophrenia compared with controls. Hippocampal volume findings were mixed. CONCLUSIONS: Studies have not found higher rates of AD-related pathology in cognitively impaired individuals with schizophrenia compared with controls. Higher rates of dementia identified in population studies may reflect a lack of specificity in clinical diagnostic tools used to diagnose dementia.
Biomarkers , Schizophrenia , Humans , Schizophrenia/cerebrospinal fluid , Schizophrenia/pathology , Biomarkers/cerebrospinal fluid , Neurodegenerative Diseases/cerebrospinal fluid , Neurodegenerative Diseases/pathology , Neurodegenerative Diseases/diagnostic imaging , Neurodegenerative Diseases/diagnosis , Alzheimer Disease/cerebrospinal fluid , Alzheimer Disease/pathology , Alzheimer Disease/diagnostic imaging , Alzheimer Disease/diagnosis , Amyloid beta-Peptides/cerebrospinal fluid , Amyloid beta-Peptides/metabolism , Neurofibrillary Tangles/pathology , Plaque, Amyloid/pathology , Plaque, Amyloid/diagnostic imaging
INTRODUCTION: There is increasing emphasis on the importance of optimizing and standardizing clinical trials of agitation in Alzheimer's disease (AD), but the risks of bias arising from published trials and the number and design of unpublished studies are poorly understood. METHODS: Using the ClinicalTrials.gov database, we systematically reviewed all registered investigational clinical trials for agitation in AD to describe the landscape of agitation drug treatment trials and to assess their quality and generalizability. RESULTS: We included 52 clinical studies registered over the past 25 years. Within published randomized controlled trials (RCTs), there was a high rate of participant dropout, poor reporting of randomization procedures, and inconsistent definitions of the sample included for analysis. There was also evidence of publication and funder bias. DISCUSSION: We discuss factors that limit the internal and external validity of published RCTs and make additional recommendations for the conduct and reporting of future clinical trials of agitation in AD.
